Back plate



FIG. 1 is a right perspective view of a back plate showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken line portions in the drawings are for illustrative purposes and do not form a part of the claimed design. 

The ornamental design for a back plate, as shown and described. 